Rescue workers move a body from the site of a blast outside a public park in Lahore, Pakistan, March 27, 2016.REUTERS/Mohsin Raza

A breakaway Pakistani faction of the Taliban group has claimed responsibility for an Easter Sunday bombing in a public park in the eastern city of Lahore that was packed with people celebrating the religious day. The explosion killed up to 65 people and injured over 300.

Ahsanullah Ahsan, the spokesman for Jamaat-ul-Ahrar, told the Associated Press that a suicide bomber with the faction had deliberately targeted the Christian community. The explosion took place near the children's rides in Gulshan-e-Iqbal Park.

"It was our people who attacked the Christians in Lahore, celebrating Easter, the spokesman said. "It's our message to the government that we will carry out such attacks again until Sharia Islamic law is imposed in the country," he added.

Ahsan warned that that the militants would strike again in Punjab. The group broke away from the Pakistani Taliban in 2014 following infighting between the top commanders. Jamaat-ul-Ahrar rejoined the Taliban in March 2015 but still maintains its own faction within the group.

Christians make up about 1% of Pakistan's total 190 million population. They have a greater presence in Lahore.

Local police chief Haider Ashraf said that the explosion appeared to have been a suicide bomber. Initial forensic investigation into the attack revealed that the suicide bomber had packed more than 20 pounds of explosives in his vest. Ball bearings, which are typically used in bomb attacks to maximise casualties were also found in the scene, Ashraf said.

"We can say it was a suicide blast, in which most of the Christian families and Muslim families who went to Gulshan-e-Iqbal Park to enjoy the holiday were targeted. He said that the suicide bomber had denoted his explosives near an area marked off for women.

The park was manned by police and private security guards, Asraf said. "We are in a warlike situation and there is always a general threat but no specific threat alert was received for this place," he said.

Punjab's Chief Minister Shahbaz Sharif said three days of mourning and pledged to bring the perpetrators to justice, said Zaeem Qadri, a spokesman for the provincial government. Schools and business in the city will remain closed on Monday, the city's schools association and the Union of Lahore Traders said.

Sharif promised to bring the culprits to trial. "Those who targeted innocent citizens do not deserve to be called humans," he said on his Twitter account. "We will hunt you down," he said, adding that he will "make sure your interior infrastructure is dismantled completely."

Prime Minister Nawaz Sharif held a meeting to assess the security situation in Lahore, according to a government statement. Pakistan's army chief, General Raheel Sharif has also convened an emergency meeting of the country's intelligence agencies to start investigations, said an army spokesman General Asim Saleem Bajwa.